The current version of Plex Desktop is 1.92.1. The current version of Plex HTPC is 1.60.1 via Flathub and 1.61.1 via Snap.
Also, Plex Media Server and the 6.8 kernel do not yet play nice together due to Intel driver issues (thread). There might be some spillover for the desktop apps.
You might try updating to the most current release available.
Also, check Settings → Plex for Windows → Player + Show Advanced. If enabled, try disabling Use Hardware Decoding.
